The present invention relates generally to the purification of contaminated fluids used on high-production machining operations and more particularly to a system for coalescing and separating insoluble soaps and reverse phase emulsions from a soluble oil emulsion utilized as a cutting fluid in industrial operations.
Industrial machining processes or systems often generate excessive heat and friction during operation. Typically, a soluble oil is employed as a coolant and lubricant in such processes or systems in order to attenuate the amount of heat and friction generated, for example, during a cutting operation. Soluble oil is an oil-in-water emulsion in which water is the continuous phase and oil is the disperse phase. The oil droplets dispersed in the water average approximately 0.5 microns in size.
Soluble oil emulsions also require emulsifying agents, such as water-soluble soaps and detergents, which have a general structure of a hydrophobic paraffin chain terminating in a hydrophilic polar group. The emulsifying water-soluble soaps effectively stabilize the oil-in-water emulsions. More specifically, the hydrophobic paraffin chains concentrate in the oil droplets while the hydrophilic polar groups, which contain sodium or potassium cations, are oriented toward the continuous water phase. Because the sodium or potassium cations on the polar groups of the emulsifying soaps establish similar charges on the surface of the respective oil droplets, the oil droplets engage in a Brownian motion and repel each other. The emulsifying soaps therefore hold the oil droplets in a stable suspension in the water by preventing the oil droplets from coalescing.
In forming the emulsion, the water that is mixed with the neat soluble oil is typically a "hard" water and therefore contains impurities such as and calcium bicarbonate. In addition, other hard impurities such as raw, fine aluminum or iron containing particles become entrained in the emulsion during operation. The hard impurities are problematic because an undesirable ion exchange is often established which causes ions such as calcium from the hard impurities to displace the sodium and/or potassium ions in the emulsifying soaps. Initially, the oil droplets enter a transitional "partially spent" phase in which the emulsifying soaps contain some sodium ions and some calcium ions on the polar groups. In this "partially spent" transitional phase, the emulsifying soaps maintain positive charges on the polar groups and are still by and large effective in maintaining a stable emulsion.
However, the amount of hard impurities entering the soluble oil increases dramatically over time. In production operations, neat soluble oil is mixed with water in ratios generally ranging from about 10:1 to about 40:1, depending upon the amount of lubrication and/or cooling necessary for the operation. The concentration of hard impurities present in the water may range from approximately 50 ppm to as high as 400 or more ppm. Because the production operations generate heat, water must be continually added to the soluble oil to compensate for evaporation. Each time that water is added, the concentration of calcium-containing impurities in the soluble oil increases, and the aforementioned undesirable ion exchange becomes more frequent.
As the concentration of hard impurities in the soluble oil emulsion increases, some of the emulsifying soaps on the transitional phase oil droplets are rendered completely insoluble as more sodium ions on the polar groups are replaced by, for example, calcium ions. The presence of a water-insoluble emulsifying soap on the surface of an oil droplet causes the oil droplet to reverse into a water-in-oil emulsion because the inner portion of the droplet has a greater wetting power than that of the outer portion. Thus, water-insoluble soaps, such as calcium soaps, stabilize water-in-oil emulsions, as opposed to stabilizing the desired normal oil-in-water emulsions.
Contamination of the normal oil-in-water soluble oil by these insoluble soaps and reverse phase emulsions has heretofore been a large problem. More specifically, the reverse phase emulsions destroy the stability of the normal soluble oil emulsion. The reverse phase emulsions are attracted to the partially-spent-but-still-effective transitional oil droplets, thereby immobilizing the partially spent oil particles. In addition, where as the normal oil-in-water emulsion has very minimal attraction to air, the insoluble soaps and reverse phase emulsions are conversely greatly attracted to air, thereby creating a harmful foam on the surface of the soluble oil coolant. The foam engulfs solid particles, such as the aforementioned aluminum oxide, which are often abrasive and are difficult to remove from the soluble oil coolant because the foam prevents the solid particles from settling.